Process of making nickel steels



li atentecl May 2, 11933 tantra oaarca FREDERICK M. B i

I T, OF NEW YORK, N. 22, ASSIGNOR T ELEGTRO METALLURGICAL GOWANY, A GORPORATION 0F WEST PROCESS OF NG NICKEL STEELS Ito Drawing.

The invention is a process for the manufacture of nickel steels, of which there are a number of commercial varieties. There are, for example, the high-strength nickel and chrome-nickel steels much used in the automotive industries; the steel containing about 35% of nickel which is known commercially as invar; and the chromium-nickel stainless steels, of which a composition containing about 18% of chromium and 8% of nickel is typical. The invention is especially' concerned with steels of the stainless class, carryin with nickel, enough chromium to ren er them strongly resistant to 1 corrosion, but it is also applicable to the manufacture of other nickel steels.

Alloying metals are usually introduced into a steel by adding them in themetal lic state. Thus, in making the stainless chroadded as ferrochrome. In other processes of making alloy steels, usually called direct processes, a chemical compound of an alloying metal is reduced in the presence of a steel bath, with which the alloying metal is thereby incorporated. Direct processes have recelved special attention for the making of stainless steels, but only for the introduction of the chromium. In making nickel steels, the nickel is always added in previously reduced form, as commercially pure nickel or a nickel alloy, even when chromium is introduced into the same steel by a direct method.

According to the present invention the nickel content of a nickel steel is provided by decomposing matte .(nickel sulphide) with silicon in the presence of a steel bath. An important saving is thereb efiected, the price of a unit of metallic. nic el being considerably higher than the price of an equal uantity ofnickel in the form of matte. lhe reaction between heavy metal sulphides and silicon, whereby the former are reduced, is not unknown, but so far as I am aware, there is no indication in the prior art that the reaction is available for the-direct production of nickel steels sufficiently low in sulphur to meet the most rigorous specifica- 59 tions.

mium-nickel steels, the chromium is usually- Application filed. November 18, 1930. Serial No. 496,570.

lhe silicon used to reduce the nickel matte may be in. the form of commercial silicon or ferrosilicon, but in many cases it is advantageous to use a silicon alloy which itself contains an alloying metal to be introduced into the steel. Thus, if nickelsilicon or ferronickel-silicon is used to reduce the nickel matte, both the matte and the reducing agent will contribute nickel to the steel. The reducing agent may also to contain other alloying metals, tfor example chromium, together with, or instead of nickel. Any metal associated with the silicon in the reducing agent will of course pass into the steel.

A serious difliculty in making stainless steels arises out of the fact that the carbon content of these compositions must be very low indeed. To make steels sufficiently low in carbon by the present invention, it is necessary to use reducing agents containing enough silicon to render them substantially carbon-free. Commercial silicon and the grades of ferrosilicon which are high in silicon do not carry enough carbon to cause any '75 trouble, but if a considerable percentage of chromium is present in the reducing agent, its tendency to take up carbon is so great that the silicon content of the reducing agent must be high, usually 30% press the carbon content sufliciently. When the reducing agent is a nickel-silicon or ferronickel-silicon alloy containing-little or no chromium, a silicon content of 25% is usually adequate. Practically carbon-free ferrochrome-silicon, which is an excellent reducing agent for use in the present process as applied to the manufacture of chromiumcontaining nickel steels, and particularly stainless steels, can be made by simultane- 9o ously reducing chromite and silica with carbon in the electric furnace. Nickel matte, reduced with carbon under ordinary furnace conditions, gives metal so contaminated with carbon and sulphur as to be useless for steelmaking, but if silica is reduced with the matte, a low-carbon low-sulphur nickel-silicon alloy is produced which may be used to great ad vantage as the reducingagent of the hereinde-; scribed invention. Following this modificaor more, to de- 80 tion, nickel derived from matte in two different ways, one through the medium of nickel-silicon and the other directly from the matte with which the nickel-silicon is made to react, is introduced into the nickel steel produced. It is also within the invention to reduce a compound of any other alloying metal, such as chromite, with nickel matte and silica and thus to prepare a educing agent containing a plurality ofalloying metals.

The invention will now be more particularly described as applied to the manufacture of stainless chromium-nickel steels, the chromium as well as the nickel being introduced by a'direct process.

Chrome ore, nickel matte, and a siliconcontaining reducing agent'areused, and are preferably ground to pass an 8-mesh screen. It may be advantageous in some cases to divide the materials into two separate batches, one consisting of chrome ore and siliconcontaining reducing agent, and the other of nickel matte and reducing agent; or the chrome ore, nickel matte and reducing agent are all charged together. In any event, the reducing and reducible materials are well mixed. Lime is added for fluxing purposes and it may be advisable in some cases to add pther fluxes, such as fluorspar. The mixture is charged into an open-arc electric furnace of the conventional type at such a rate that the smelting takes place in a uniform manner, and a fluid bath of slag is maintained at all times. A low-carbon steel bath may be placed in the furnace before the starting of smelting, either by melting steel scrap and decarburizing if necessary, or by supplying the furnace with molten metal from a Bessemer or open-hearth furnace. Alternatively, steel scrap may be incorporated with the smelting charge, or even supplied to the furnace after the smelting has been completed. The iron added in the form of chrome ore or a ferro-alloy of the silicon-containing reducing agent may of course be sufiicient in some instances to yield the desired iron content in the product The above-described ways of adding iron are intended to be included in the expression and adding iron used in the appended claims.

In order to insure the production of a lowsulphur alloy, it is advisable to operate with a slag of considerable basicity. Expressed in terms of the ratio of CaO to SiO it is desirable to keep this ratio at least 2 to 1, and ratios of 3 to 1 or higher maybe satisfactorily employed. In cases where extermely high degrees of basicity are used, it is helpful to control the fluidity of the slag by means of fluorspar additions.

The following example illustrates the production of a heat of so-called 188 stainless steel, and is typical of the results to be obtained by my improved direct process.

A bath of steel was melted in an electric steel furnace, and by the use of an oxidizing slag was decarburized to 0.02% carbon. Most of the oxidizing slag was poured off, after which another slag was made by melting together lime and a little fluorspar. A batch of the following composition was then charged into the furnace:

, Parts Chrome ore 141 75% ferrosilicon 34. Lime 150 The chrome ore contained 33.94% chromium. The ferrosilicon and lime were of usual commercial quality. Upon completion of the furnacing of this batch, a nickel-containing batch of the following composition was charged into the furnace:

Parts Nickel matte 24 75% ferrosilicon 6 Lime 30 Analysis of the steel is shown below:

The slags were satisfactorily low in chromium and nickel, 80% of the chromium and 97% of the nickel being recovered in the finished metal.

Following are the results of physical tests made on specimen test pieces taken from ingots cast from the above-described heat. The test pieces were quenched from 1150 C.

Maximum stress 112,500 lbs. per sq. in. Yield point 32,000 lbs. per sq. in. Elongation 52% Reduction of area 60% Impact 111 ft. lbs-bend Erichsen value 12.5 Brinell hardness 143 rial, with a silicon alloy containing at least one metal of the group: iron, nickel, chromium; and adding iron.

2. A process of making nickel-chromium steels which comprises reducin nickel matte, in the presence of basic slag-Forming material, with a silicon alloy containing chromium; and adding iron.

3. A process of making nickel-chromium steel which comprises simultaneously reducing nickel matte and chromite with ferrochrome silicon in the presence of a basic slag.

4 A process of making stainless steel which comprises reducing nickel matte with ferrochrome silicon containing at least 30% of silicon in the presence of a basic slag.

5. A process of making nickel-containing steels which comprises reducing nickel matte and silica simultaneously with carbon to form a low-carbon nickel-silicon alloy, re clucing with this alloy a second lot of nickel matte in the presence of basic slag-forming material, and adding iron.

6. A process of making nickel-containing steel which comprises reducing nickel matte witha substantially carbon-free silicon alloy under a strongly basic slag, and adding iron.

7. A process of making stainless steel which comprises reducing chromite and nickel matte with a ferrochrome silicon containing at least about 30% of silicon, the reduction of the matte being carried out under a strongly basic slag.

8. A process of making nickel-containing steel which comprises reducing nickel matte with silicon under a strongly basic slag, and adding iron.

9. A process of making nickel-containing steel which comprises reducin nickel matte, in the presence of basic slagorming material, with a silicon alloy containing iron and at least one metal of the group: nickel, chromium.

10. A process of making nickel-chromium steel which comprises reducing nickel matte and chromite simultaneously, in the presence of basic slag-forming material, with a silicon alloy containing iron and at least one metal of the group: nickel, chromium.

11. A process of making nickel-chromium steel which comprises reducing nickel matte and silica simultaneously with carbon to form a low-carbon nickel-silicon alloy, and reducing with this alloy, in the presence of basic slag-forming material, chromite and a second lot of nickel matte.

12. A process of making nickel-chromium "h steel which comprises reducing nickel matte with a silicon alloy containing chromium, in the presence of a steel bath and basic slag-forming material.

In testimony whereof, I aflix my signature.

FREDERICK M. BECKET. 

